The present invention relates generally to networks and, more particularly, to systems and methods for selecting a cell in a wireless communications network.
At startup, a mobile terminal may perform a cell search operation to find, identify, and synchronize to a cell in the communications network. In a wideband code division multiple access (WCDMA) network, this cell search operation may consist of a three-stage pipeline process, as described, for example, in xe2x80x9cCell Search in W-CDMA,xe2x80x9d by Yi-Pin Eric Wang et al., IEEE J. Select. Areas Commun., Vol. 18, No. 8, August 2000, pp. 1470-1482.
The goal of the three-stage pipeline process is to achieve time and code synchronization. In stage 1, the mobile terminal generates a slot boundary candidate. Stage 2 of the pipelined process receives the slot boundary candidate and identifies a frame boundary and scrambling code group pair. Finally, in stage 3, the mobile terminal uses the frame boundary-code group pair to identify a scrambling code. The mobile terminal may perform a verification and termination operation in stage 3 to determine a confidence score of the candidate scrambling code. When the mobile terminal detects a candidate with a high confidence score, the mobile terminal may perform a frequency acquisition operation. When a candidate having a high confidence score is not detected in stage 3, the mobile terminal continues the pipeline process.
Systems and methods, consistent with the present invention, facilitate the selection of a cell in a wireless communications network.
In accordance with the invention as embodied and broadly described herein, a method for selecting a frequency error estimate in a wireless communications network is provided. The method includes generating a slot boundary candidate, identifying a frame boundary and scrambling code group for the slot boundary candidate, identifying a scrambling code from the identified scrambling code group, determining a frequency error estimate using the identified scrambling code, determining a detection metric, comparing the detection metric to a predetermined threshold, and selecting the frequency error estimate when the detection metric is greater than the predetermined threshold.
In another implementation consistent with the present invention, a system for selecting a frequency error estimate in a WCDMA system is provided. The system includes a first stage that generates a slot boundary candidate, a second stage that receives the slot boundary candidate and identifies a frame boundary and scrambling code group, a third stage that receives the scrambling code group and identifies a scrambling code, and a fourth stage that receives the scrambling code, determines a frequency error estimate using the scrambling code, generates a detection metric, and selects the frequency error estimate when the detection metric exceeds a threshold.
In yet another implementation consistent with the present invention, a four-stage pipelined system is disclosed. The pipelined system includes a first stage that detects a slot boundary, a second stage that receives the slot boundary and identifies a frame boundary and scrambling code group based on the slot boundary, a third stage that receives the frame boundary and scrambling code group and identifies at least one scrambling code based on the frame boundary and scrambling code group, and a fourth stage that receives the scrambling code and performs frequency acquisition and cell search verification and termination.